An experiment gone awry sends the Doctor (Jon Pertwee) to a parallel universe where his friends and companions are members of a fascist regime in this thrilling and popular episode from the long-running science fiction series Doctor Who. Inferno is the name of a project designed to drill into the Earth's core and release a powerful energy source called Stahlman's Gas; what's yielded instead is an insidious substance that transforms men into monsters. The resulting chaos interrupts the Doctor's travel in the TARDIS and knocks him into an alternate Earth run by a military dictatorship, and where Project Inferno's progress threatens to bring about an apocalypse. This seven-part story arc from 1970 is a high-water mark for the already superb Pertwee-era Doctor, a tense, imaginative adventure that evokes the U.K.'s chilling Quatermass TV productions and movies in its mix of science fiction and horror. Fans will particularly appreciate the opportunities afforded to longtime Who supporting players Nicholas Courtney (as the Brigadier) and Caroline John (as the Doctor's companion Liz) to step outside their usual roles and essay memorably villainous turns as their parallel-Earth selves. The double-disc presentation of Inferno offers the by-now-standard wealth of extras, including commentary by Courtney, script editor Terrance Dicks, producer/director Barry Letts, and co-star John Levene (Sgt. Benton) and lengthy featurettes on the making of the story and the UNIT brigade during Pertwee's tenure (the latter featuring interviews with much of the supporting cast and crew). A short deleted scene from the episode (featuring Pertwee in a rare second turn as the voice of a radio announcer), a promo film for the BBC Visual Effects Department (which features clips from the Who stories Ambassadors of Death, Caves of Steel, and a missing episode from Doomwatch), and PDF files of the 1971 Doctor Who Annual and Radio Times round out the supplemental features. --Paul Gaita